Pressure retard switch



1, 1967 J. P. BRENNY ETAL 3,334,204

PRESSURE RETARD SWITCH Filed Sept. 9, 1965 VOLTAGE SOURCE l INVENTOR. JEROME F. BRENNY JAY N. HOPPS JR. BY CHARLES W. LINDBERG ATTORNEY United States Patent 3,334,204 PRESSURE RETARD SWITCH Jerome P. Brenny, Hopkins, Jay N. Hopps, Jr., Minneapolis, and Charles W. Lindberg, Hopkins, Minn., assignors to Honeywell Inc., Minneapolis, Minn., a corporation of Delaware .Filed Sept. 9, 1965, Ser. No. 486,168

6 Claims. (Cl. 200-82) ABSTRACT OF THE DISCLOSURE This invention relates generally to the art of timing devices and more specifically concerns the design of a timing device in which a gas generator is utilized to produce a high pressure within a closed chamber, the gas in the chamber then being allowed to escape at a controlled rate through a restrictor assembly.

Various mechanical, electrical and chemical timing devices have been devised for use in the many systems in which it is necessary to provide a means for establishing a certain period of time between the occurrence of two events. The present invention, an interval timer, is primarily useful in those applications that require a nonreusable, one-shot timer. Most systems in which timing devices are used require that the timing device be resettable. For those applications, the usual clock escapement mechanism or fluid dash-pot type of system may be applicable. In other systems, only a single timing action is required. For example, many military applications utilize one-shot timers. In munition fuzing it is common practice to incorporate a timing device to assure that a The present invention utilizes the basic principle of a fluid being metered through an orifice at a controlled rate to obtain a timing action. Although-the basic principle is well known, the present invention provides avunique method of generating a known quantity of gas that is allowed to escape from a closed chamber at a controlled rate. Since the size of the chamber'is fixed, the quantity of gas isknown, and the size of the orifice is known, the

time required for the gas to escape from the chamber can be accurately predicted. a

The present invention has many advantagesover oneshot timers disclosed in the prior art. Because of its simplicity, it can be easily manufactured; It has only a single moving part, that part being a pressure sensing device. Even that could be modified to eliminate much of the movement. Because of the fact that the pressure is generated only when the deviceis being used, a pressure storage vessel isjnot required. There are thus noproblems with leakage should storage for a long period of time be necessary. This device can also-be packed in a very small container because of its inherentsimplicity. The timed interval can also be easily changed by changing the various parameters of the timer design.For example, the

pressure sensing device can be changed to respond to a different level of pressure to obtain a different time interto provide a one-shot timing device in'which a gas generator is mounted in a closed chamber, the gas being generated only at the time the device is being utilized as a timer to thereby generate a known pressure within the chamber, the gas being allowed to escape from the chamber through a restrictor assembly at a controlled rate to establish the timed period.

Other objects of the invention will become apparent from the following specification and claims, and from the accompanying drawing, wherein the single figure is a sectional, side view of the preferred embodiment of'the interval timer in the non-actuated position.

The cross-sectional side view of the timing device illustrated in the accompanying drawing discloses all of the elements of the invention. The timing device includes a tubular or cylindrical housing member 10 having a chamber 11 formed therein with a first'open end 12 and a second open end 13. Although housing member 10 is formed in the shape of a cylinder in the preferred embodiment of the invention, the particular configuration is not critical. Mounted within first end 12 of housing member 10 is a fluid restrictor assembly 14. Fluid restrictor assembly 14 has a central opening 15 through which a gas contained within chamber 11 can escape to the exterior of housing member 10.

Mounted across opening 15 of restrictor assembly 14 is a silicone rubber restrictor 16. Restrictor 16, being composed of silicone rubber in the preferred embodiment, is thus a permeable or porous material that will allow air or other gases to pass from chamber 11 to the outside of housing member 10. Since the pores in restrictor 16 are quite small, the gas flow therethrough is relatively slow. Under normal storage conditions, the pressure within chamber 11 is the same as atmospheric pressure since air will dilfuse through permeable restrictor 16 to equalize the pressure on both sides thereof. Although silicone rubber is used as the restrictor material in the preferred embodiment of the invention, other permeable material such as polystyrene film could be utilized to vary the rate of air flow from chamber 11.

Since restrictor 16 is manufactured from rathera flexible material, it must be supported so that the high pressure that is developed within chamber 11 will not destroy its integrity. A sintered metal or other porous downstream filter member 17 is thus mounted between restrictor 16 and open end 12. Filter 17 is much more porous than restrictor 16 so that air or gas will pass freely through it. Since filter 17 is non-flexible, however, it will prevent the collapse of restrictor 16 when pressure is applied.

If necessary for the particular application, an upstream filter 18 can be mounted between restrictor 16 and chamber 11. Filter 18 is also manufactured from a sintered metal or other solid porous material that will allow air or gas to pass relatively freely through it. Filter 18 provides at least three functions in the operation of this device. First, filter 18 physically supports flexible restrictor 16. Secondly, filter 18 acts as an upstream filter to prevent large particles of dust or other foreign material from reaching restrictor 16. Because of the relatively impervious nature of restrictor 16, it is important that large particles of foreign material not be allowed to impinge thereon. Thirdly, filter 18 acts asa heat sink to absorb heat from the hot gas that is generated within chamber 11.

The hot gas, if directly applied to' restrictor 16, could cause damage to it. Tests conducted with the PG-l propellant indicate that filter 18 is not required in all cases. The gas temperatures generated with the PG-l propellant were not high enough to damage the silicone rubber and no dust or other particles were generated to plug restrictor 16. However, filter 18 would be required if a propellant were used that burned at higher temperatures or created undesirable residue.

Mountednear the center of chamber 11 is a gas generating assembly 19. The gas generating assembly is mounted on a support member 20 having a series of holes such as21 formed therein so that the gas within the chamber 11 can pass freely around the gas generating assembly. Gas generating assembly 19 includes a casing 22 having a pellet 23 of solid propellant material mounted therein. Mounted adjacent propellant material 23 is a bridge wire 24. A pair of electrodes 25 and 26 extend through casing 22 and are connected to the ends of bridge wire 24. A second pair of electrodes 27 and 28 extend through housing and are connected to electrodes 25 and 26 respectively. Connected across electrodes 27 and 28 is a voltage source 29 and a switch 30.

When switch 30 is closed, voltage source 29 is connected across bridge wire 24. A current thus flows through bridge wire 24 to heat or explode the bridge wire. When bridge wire 24 is heated, solid propellant 23 is ignited to produce a known quantity of gas. In the preferred embodiment of the invention, a solid propellant having the trade name PG-l manufactured by Amoco is utilized. This propellant is a mixture of silver'carbonate and carbon that, when ignited, generates pure carbon dioxide gas leaving a residue of silver and carbon: The yield of carbon dioxide gas is 24% by weight. Other propellant materials could also be utilized since the type of gas is not critical to the invention. In order to minimize delay time variations, however, it is desirable to select a combination of restrictor material and gas that is compatible. For example, the combination of silicone rubber with CO gas will minimize delay variations with temperature as will the combination of polystyrene film and nitrogen gas.

Attached to second open end 13 of housing 10 is a pressure responsive switching device 32 to indicate the pressure variations occurring within chamber 11. Switching device 32 is attached by means of a threaded portion to a similarly threaded cylindrical extension 33 of housing 10. Switching device 32 includes a pair of normally open .contacts 34 and 35 and a pair of normaally closed contacts 36 and 37. A common contact 38 is attached to an operating rod 39 that extends through a support member 40 within switching device 32. The opposite end of rod 39 is connected to a piston member 41 that lies in line with open end 13. Mounted between piston 41 and support 40 is a coiled spring 42 that holds common contact 38 against normally closed contacts 36 and 37 under normal conditions. Mounted between piston 41 and open end 13 is a flexible diaphragm 43 that prevents air or gas from escaping from chamber 11'. Diaphragm 43 is firmly sealed into the connection between switch 32 and housing extension 33.

Operation- Under normal storage conditions the subject timing device remains in the position or condition shown in the drawings. Switch 30 is open so that no voltage is applied to bridge wire 24. The pressure within chamber 11 is the same as the pressure outside of housing 10 since air can difiuse through restrictor 16. Common contact 38 is connected across normally closed contact 36 and 37 to indicate this status.

When it is desired to begin the timinginterval, switch 30 is closed. Current from voltage source 29 passes through bridge wire 24 to cause ignition of pellet 23. When pellet 23 ignites, a large volume of carbon dioxide gas is formed that is trapped within chamber 11. In the preferred embodiment of this device, the initial pressure within chamber 11 is approximately 500 p.s.i.

The high initial pressure within chamber 11 causes piston 41 to compress spring 42. Diaphragm 43 flexes to allow this movement of piston 41. Diaphragm 43 continues to seal chamber 11 to prevent escape of the gas. When spring 42 is compressed, common contact 38 is driven against normally open contacts 34 and 35 to complete a circuit between them. Suitable circuitry (not shown) can be connected to contacts 34 and 35 to indicate the beginning of the time-interval.

The pressure within chamber 11 immediately begins to dissipate as the gas escapes through restrictor assembly 14. The gas within'chamber 11 is at a relatively high temperature because of the reaction of pellet 23. As previously mentioned, upstream filter 18, if used, tends to absorb most of this heat before the gas reaches restrictor 16. Filter 18 also filters out any products of combustion that would tend to clog the pores in restrictor 16.

As the gas pressure within chamber 11 decays, spring 42 will tend to overcome the pressure acting against piston 41. At a predetermined reduced pressure, spring 42 drives piston 41 to the position shownfin the'drawing so that normally closed contacts 36 and 37 are again connected. This return of common contact 38 to the original position indicates the end of the time interval. It can be seen that the size of piston 41 and the strength of spring 42 can be adjusted so that the time interval is ended at any predetermined reduced pressure within chamber 11. In the actual embodiment of the-device, the switching device was designed to return to its normal position when the pressure within chamber 11 was equal to 40 p.s.i. The particular switching device that is disclosed in the drawing is not critical to the invention. Many other switching arrangements or signal output'devices-could be substituted without departing from the invention.

Tests have shown that the timing period can be accurately controlled and also adjusted from unit to unit by carefully controlling the device parameters. An actual model of the device has provided a time delay of 72 hours. The housing on that device displaced a volume of one-half cubic inch.

From the above description, it will be apparent that we have invented a novel timing device. Although the form of the invention described herein constituted a preferred embodiment, it will be understood that changes may be made within the spirit of the invention limited only by the scope of the appended claims.

We claim as our invention:

1. A timing device, comprising:

(a) a cylindrical housing member having a chamber therein with first and second opposite open ends;

(b) a fluid restrictor assembly mounted in said first open end including a silicone rubber restrictor to restrict the fiow of a gas from said chamber, a porous downstream filter mounted adjacent said open end to support said silicone rubber restrictor, and a porous upstream filter mounted adjacent said chamber to act as a preliminary filter and as a heat sink to absorb heat from a gas passing through said restrictor assembly;

(c) a carbon dioxide generator mounted in said chamber including a pellet of solid propellant material having a metal bridge wire mounted adjacent thereto;

(d) a pair of metal electrodes mounted in said housing member and connected to opposite ends of said bridge wire;

(e) means including pressure sensing means mounted in said chamber at said second end to seal said second open end and to provide an output indicative of the pressure in said chamber;

(f) means for impressing a voltage across said electrodes to heat said bridge wire and ignite said propellant material, said propellant material when ignited generating a known quantity of carbon dioxide to thereby increase the pressure in said chamber, said carbon dioxide flowing through said restrictor as sembly at a controlled rate to decrease the pressure in said chamber; and

(g) means responsive to the output from said pressure sensing means to signal the time required for the pressure to decay to a predetermined level.

'2. A timing device, comprising: I

(a) a housing member having a cylindrical. chamber therein with first and second open ends;

(b) a fluid restrictor assembly mounted in said first end including permeable restrictor means to restrict the flow of a gas therethrough and a downstream filter member mounted adjacent said open end to support said permeable restrictor means;

(c) gas generating means mounted in said chamber including a pellet of solid propellant material and a bridge wire;

(d) a pair of conductors mounted in said housing member and connected to opposite ends of said bridge wire;

(e) means including pressure sensing means mounted in said chamber at said second end to seal said second end and to provide an output indicative of the gas pressure in said chamber;

(1) means for impressing a voltage across said conductors to heat said bridge wire and ignite said propellant material, said propellant material thereby generating a known quantity of gas to increase the pressure in said chamber, said gas flowing through said restrictor assembly to decrease the pressure in said chamber; and

(g) means responsive to the output from said pressure sensing means to signal the time required for the pressure to decay to a predetermined level.

3. A timing device, comprising:

(a) a housing member having a chamber therein with first and second open ends;

(b) fluid restrictor means mounted in said first open end to restrict the flow of a gas from said chamber;

(c) a gas generator mounted in said chamber including a pellet of solid propellant material having a metal bridge wire mounted in close proximity thereto;

(d) a pair of electrodes mounted in said housing member and connected to opposite ends of said bridge wire;

(e) means for impressing a voltage across said electrodes to ignite said propellant material, said propellant material when ignited generating a known quantity of gas to thereby increase the pressure in said chamber, said gas flowing through said restrictor means at a controlled rate to decrease the pressure in said chamber; and

(f) means including pressure sensing means mounted in said chamber at said second end to seal said second open end and to provide an output indicative of the time required for the gas pressure in said chamber to decay to a predetermined level.

4. A timing device, comprising:

(a) a housing member having a chamber therein;

(b) a fluid restrictor assembly, mounted in an opening in said housing member, including permeable restrictor means to restrict the flow of a gas from said chamber and a downstream filter member to support said permeable restrictor means;

(c) gas generating means mounted in said chamber;

(d) means including pressure sensing means mounted in said housing member to provide an output indicative of gas pressure in said chamber;

(e) means for initiating said gas generating means to thereby generate a quantity of gas to increase the pressure in said chamber, said gas flowing through said restrictor assembly to decrease the pressure in said chamber; and

(f) means responsive to the output from said pressure sensing means to signal the time required for the pressure to decay to a predetermined level.

5. A timing device, comprising:

(a) a housing member having a chamber therein;

(b) fluid restrictor means mounted in said housing member to restrict the flow of a gas from said chamber; (c) gas generating means mounted in said chamber including a pellet of solid propellant material;

(d) means including pressure sensing means mounted in said housing member to provide an output indicative of the time required for the pressure in said chamber to decay to a predetermined level; and

(e) means for igniting said propellant material, said propellant material thereby generating a known quantity of gas to increase the pressure in said chamber, said gas flowing through said restrictor means to decrease the pressure in said chamber.

6. A timing device, comprising:

(a) a housing member having a chamber therein;

(b) fluid restrictor means mounted in said housing member to restrict the flow of a gas from said chamber;

(c) gas generating means mounted in said chamber;

((1) means for initiating said gas generating means to thereby generate a known quantity of gas to increase the pressure in said chamber, said gas flowing through said restrictor means to decrease the pressure in said chamber; and

(e) means including pressure sensing means mounted in said housing member to provide an output indicative of the time required for the pressure in said chamber to decay to a predetermined level.

References Cited UNITED STATES PATENTS 419,902 1/1890 Wider 200-142 2,712,575 7/1955 Kiel 200-142 2,721,240 10/1955 Filbert 200-142 2,816,196 12/1957 Daudelin 200-82 3,236,961 2/1966 Kappel 200-34 BERNARD A. GILHEANY, Primary Examiner.

H. B. GILSON, Assistant Examiner. 

1. A TIMING DEVICE, COMPRISING: (A) A CYLINDRICAL HOUSING MEMBER HAVING A CHAMBER THEREIN WITH FIRST AND SECOND OPPOSITE OPEN ENDS; (B) A FLUID RESTRICTOR ASSEMBLY MOUNTED IN SAID FIRST OPEN END INCLUDING A SILICONE RUBBER RESTRICTOR TO RESTRICT THE FLOW OF A GAS FROM SAID CHAMBER, A POROUS DOWNSTREAM FILTER MOUNTED ADJACENT SAID OPEN END OT SUPPORT SAID SILICONE RUBBER RESTRICTOR, AND A POROUS USPTREAM FILTER MOUNTED ADJACENT SAID CHAMBER TO ACT AS A PRELIMINARY FILTER AND AS A HEAT SINK TO ABSORB HEAT FROM A GAS PASSING THROUGH SAID RESTRICTOR ASSEMBLY; (C) A CARBON DIOXIDE GENERATOR MOUNTED IN SAID CHAMBER INCLUDING A PELLET OF SOLID PROPELLANT MATERIAL HAVING A METAL BRIDGE WIRE MOUNTED ADAJCENT THERETO; (D) A PAIR OF METAL ELECTRODES MOUNTED IN SAID HOUSING MEMBER AND CONNECTED TO OPPOSITE ENDS OF SAID BRIDGE WIRE; (E) MEANS INCLUDING PRESSURE SENSING MEANS MOUNTED IN SAID CHAMBER AT SAID SECOND END TO SEAL SAID SECOND OPEN END AND TO PROVIDE AN OUTPUT INDICATIVE OF THE PRESSURE IN SAID CHAMBER; 